Magnetic disk device

ABSTRACT

According to one embodiment, among a plurality of magnetic heads, the larger the magnetic pole width of the magnetic pole of the magnetic head in the width direction of a recording track formed in a recording layer or the larger an area width of the magnetic head capable of reading the magnetic characteristics of an area of the recording layer on which magnetic recording has been carried out by means of the magnetic head, the farther is the magnetic head arranged outwardly from the vicinity of the center in the parallel arrangement direction of the magnetic disks.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of application Ser. No.17/168,639, filed Feb. 5, 2021 and is based upon and claims the benefitof priority from Japanese Patent Application No. 2020-085002, filed May14, 2020, the entire contents of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to a magnetic disk device.

BACKGROUND

As a means for increasing the recording capacity of a magnetic diskdevice, it is effective to increase the number of magnetic disks to beincorporated in the device. However, when the equipping space islimited, in order to increase the number of the magnetic disks, there isa need to reduce the thickness of the magnetic disk and interval betweenadjacent magnetic disks. Even when the thickness of the magnetic diskand interval between magnetic disks are reduced, it is required that theerror occurrence frequency should not be increased at the time of datawrite or data read due to, for example, deterioration in the positioningaccuracy of the magnetic head. The positioning accuracy of the magnetichead is subject to the influence of the torsion or the like occurring tothe rotational shaft of the actuator at the time of drive of themagnetic head, and hence the magnetic heads arranged closer to the coverside and the base side are more liable to be deteriorated in thepositioning accuracy. That is, the positioning accuracy of the magnetichead differs depending on the position in the direction (parallelarrangement direction) in which the magnetic heads are arranged inparallel with each other.

An embodiment described herein aims to provide a magnetic disk devicemaking it possible to increase the recording capacity thereof by takingthe position of a magnetic head in the parallel arrangement direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram schematically showing a hard disk drive (HDD)according to an embodiment.

FIG. 2 is a side view schematically showing a magnetic head, suspension,and magnetic disk in the HDD.

FIG. 3 is a cross-sectional view showing a head section of the magnetichead in an enlarged form.

FIG. 4 is a perspective view schematically showing a write head of themagnetic head.

FIG. 5 is a cross-sectional view showing a tip section of the write headin an enlarged form.

FIG. 6 is a plan view of the write head of the magnetic head viewed fromthe ABS side.

FIG. 7 is a view schematically showing an example of an arrangementconfiguration of the magnetic disks and magnetic heads.

FIG. 8 is a view showing a relationship between the cross-track positionand signal output to be used when a width of the magneticcharacteristics of the main pole is measured.

FIG. 9 is a view showing an example of a value of a magnetic pole widthof each of the write heads in the plurality of magnetic heads.

FIG. 10 is a view schematically showing a relationship between a writecount indicating the number of times of write to the recording track ofthe magnetic disk and error rate.

FIG. 11 is a view showing a classification example of the magnetic disksbased on the overwrite characteristics (OW).

FIG. 12 is a flowchart showing an example of control (recording-currentcontrol processing) of a recording current in the HDD.

DETAILED DESCRIPTION

In general, according to one embodiment, a magnetic disk device includesa plurality of magnetic disks and a plurality of magnetic heads. Theplurality of magnetic disks includes each a recording layer and arrangedon the same axis at intervals in juxtaposition with each other. Theplurality of magnetic heads includes each a magnetic pole configured togenerate a recording magnetic field in a direction perpendicular to therecording layer and arranged at intervals in the parallel arrangementdirection of the magnetic disks in juxtaposition with each other. Amongthe plurality of magnetic heads, the larger the magnetic pole width ofthe magnetic pole of the magnetic head in the width direction of arecording track formed in the recording layer or the larger an areawidth of the magnetic head capable of reading the magneticcharacteristics of an area of the recording layer on which magneticrecording has been carried out by means of the magnetic head, thefarther is the magnetic head arranged outwardly from the vicinity of thecenter in the parallel arrangement direction.

First Embodiment

A hard disk drive (hereinafter referred to as an HDD) according to afirst embodiment will be described in detail as a magnetic disk device.FIG. 1 is a block diagram schematically showing an HDD according to thefirst embodiment, and FIG. 2 is a side view showing a magnetic head inthe floating state and magnetic disk.

As shown in FIG. 1 , an HDD 10 is provided with a rectangular housing11, magnetic disk 12 serving as a recording medium arranged inside thehousing 11, spindle motor 21 configured to support thereon and rotatethe magnetic disk 12, and a plurality of magnetic heads 16 configured tocarry out write/read of data to/from the magnetic disk 12. The housing11 includes a rectangular box-shaped base (illustration omitted) openedat the upper part thereof, and cover (illustration omitted) to be put onthe opening of the base. The base is constituted of, for example, arectangular bottom wall and sidewall rising along the periphery of thebottom wall, and is integrally formed of aluminum or the like. The coveris screwed onto the sidewall of the base by means of, for example, aplurality of screws, air-tightly closes the opening of the base, and isformed stainless steel or the like.

The HDD 10 is provided with a head actuator 18 configured to move themagnetic head 16 to a position on an arbitrary recording track on themagnetic disk 12 and carry out positioning of the magnetic head 16. Thehead actuator 18 includes a carriage assembly 20 configured to movablysupport the magnetic head 16 thereon and voice coil motor (hereinafterreferred to as a VCM) 22 configured to rotate the carriage assembly 20.

The HDD 10 is provided with a head amplifier IC 30 configured to drivethe magnetic head 16, main controller 90, and driver IC 92. The headamplifier IC 30 is provided on, for example, the carriage assembly 20and is electrically connected to the magnetic head 16. The headamplifier IC 30 is provided with a recording-current supplying circuit(recording-current supplying section) 91 configured to supply arecording current to recording coils of the magnetic head 16,bias-voltage supplying circuit 93 configured to supply a bias voltage(drive current) to a spin-torque oscillator (hereinafter referred to asan STO) to be described later, heater-voltage supplying circuit 98configured to supply a drive voltage to heaters to be described later,amplifier (illustration omitted) configured to amplify a signal read bythe magnetic head 16, and the like.

The main controller 90 and driver IC 92 are formed on a control circuitboard (illustration omitted) provided on, for example, the backside(base side) of the housing 11. The main controller 90 is provided withan R/W channel 94, hard disk controller (hereinafter referred to as anHDC) 96, microprocessor (hereinafter referred to as an MPU) 97, andmemory 80. The main controller 90 is electrically connected to themagnetic head 16 through the head amplifier IC 30. The main controller90 is electrically connected to the VCM 22 and spindle motor 21 throughthe driver IC 92. The HDC 96 is connectable to the host 95.

As shown in FIG. 1 and FIG. 2 , the magnetic disk 12 is configured as aperpendicular magnetic recording medium. The magnetic disk 12 includes asubstrate 101 formed into a circular disk-like shape of, for example, adiameter of 88.9 mm (3.5 inches) and constituted of a nonmagneticmaterial. In each of the surfaces (top surface and undersurface) of thesubstrate 101, a soft magnetic material layer 102 functioning as afoundation layer and constituted of a material exhibiting soft magneticcharacteristics, magnetic recording layer (recording layer) 103 havingmagnetic anisotropy in the direction perpendicular to the surface of themagnetic disk 12, and protective film 104 are stacked on top of eachother from the lower layer to the upper layer in the order mentioned.The magnetic disk 12 is coaxially fitted onto a hub of the spindle motor21. The magnetic disk 12 is rotated by the spindle motor 21 at apredetermined rotational speed in the direction of the arrow B.

The carriage assembly 20 includes a bearing section 24 rotatablysupported on the housing 11 and a plurality of suspensions 26 outwardlyextending from the bearing section 24. As shown in FIG. 2 , the magnetichead 16 is supported on the extension end of each suspension 26. Themagnetic head 16 is electrically connected to the head amplifier IC 30through a wiring member (flexure) 28 provided on the carriage assembly20.

As shown in FIG. 2 , the magnetic head 16 is formed as a floating typehead, and includes a slider 42 formed into a shape approximate to arectangular parallelepiped and head section 44 formed at the end part ofthe slider 42 on the outflow-end (trailing) side thereof. The slider 42is formed of a sintered body (AlTiC) constituted of, for example,alumina and titanium-carbide and head section 44 is formed of amultilayer thin film. The slider 42 is attached to a gimbal section 41of the wiring member 28.

The slider 42 includes a rectangular disk-opposing surface (air bearingsurface (hereinafter referred to as an ABS) 43 opposed to the surface ofthe magnetic disk 12. The slider 42 is maintained in a state where theslider 42 is floated from the surface of the magnetic disk 12 by apredetermined amount by an airflow C caused between the disk surface andABS 43 by the rotation of the magnetic disk 12. The direction of theairflow C is coincident with the rotational direction B of the magneticdisk 12. The slider 42 includes a leading end 42 a positioned on theinflow side of the airflow C and trailing end 42 b positioned on theoutflow side of the airflow C. Concomitantly with the rotation of themagnetic disk 12, the magnetic head 16 runs in the arrow A direction(head running direction) relatively to the magnetic disk 12, i.e., themagnetic head 16 runs in the direction opposite to the rotationaldirection B of the disk.

FIG. 3 is a cross-sectional view showing a head section 44 of themagnetic head 16 and magnetic disk 12 in an enlarged form. The headsection 44 includes a read head (reproducing head) 54 and write head(recording head) 58 both formed by the thin film process at the trailingend 42 b of the slider 42 and is formed as a separated type magnetichead. The read head 54 and write head 58 are each covered with anonmagnetic protective insulating film 53 except a part of the slider 42exposed to the ABS 43. The protective insulating film 53 constitutes theouter shape of the head section 44.

The longitudinal direction of the recording track formed in the magneticrecording layer 103 of the magnetic disk 12 is defined as the down-trackdirection DT and width direction of the recording track is defined asthe cross-track direction CT.

The read head 54 includes a magnetoresistance effect element 55, firstmagnetic shielding film 56 and second magnetic shielding film 57 bothrespectively arranged on the leading side (inflow side) of themagnetoresistance effect element 55 and on the trailing side (outflowside) thereof in the down-track direction DT in such a manner as tointerpose the magnetoresistance effect element 55 between them. Themagnetoresistance effect element 55, and first and second magneticshielding films 56 and 57 extend approximately perpendicular to the ABS43. The lower ends of the magnetoresistance effect element 55, and firstand second magnetic shielding films 56 and 57 are exposed to the ABS 43.

The write head 58 is provided on the trailing end 44 b side of theslider 42 relatively to the read head 54. FIG. 4 is a perspective viewof the write head 58 cut along the track center of the write head 58.FIG. 5 is a cross-sectional view showing a tip section (end section onthe ABS side) of the write head 58 in an enlarged form. FIG. 6 is a planview of the write head 58 viewed from the ABS side.

As shown in FIG. 3 and FIG. 4 , the write head 58 includes a main pole(magnetic pole) 60 configured to generate a recording magnetic field inthe direction perpendicular to the surface of the magnetic disk 12,trailing shield (write shield) 62 provided on the trailing side of themain pole 60 and opposed to the main pole 60 with a write gap WG heldbetween them, leading shield 64 opposed to the leading side of the mainpole 60, a pair of side shields 63 provided on both sides of the mainpole 60 in the cross-track direction CT, and high-frequency oscillatorelement provided inside the write gap WG and between the main pole 60and trailing shield 62, for example, spin-torque oscillator element(STO) 65. The main pole 60 and trailing shield 62 constitute a firstmagnetic core forming a magnetic path, and the main pole 60 and leadingshield 64 constitute a second magnetic core forming a magnetic path. Thewrite head 58 includes a first recording coil 70 wound around the firstmagnetic core and second recording coil 72 wound around the secondmagnetic core.

The main pole 60 is formed of a soft magnetic material having highmagnetic permeability and high saturation magnetic flux density andextends approximately perpendicular to the ABS 43. The tip section 60 aof the main pole 60 on the ABS 43 side is narrowed down in such a manneras to be tapered off toward the ABS 43 and is formed into a columnarshape having a width narrower than the other parts. The tip-end face ofthe main pole 60 is exposed to the ABS 43 of the slider 42.

As shown in FIG. 5 and FIG. 6 , the tip section 60 a of the main pole 60includes a flat trailing-side end face (a shield-side end face) 60 bopposed to the trailing shield 62 with a gap held between them. The tipsection 60 a is formed into, for example, a trapezoidal shape in crosssection. The trapezoidal tip section (tip-end face) 60 a includes thetrailing-side end face 60 b extending in the cross-track direction CT,leading-side end face 60 c opposed to the trailing-side end face 60 b,and both side faces 60 d. At the ABS 43, the width of the tip section 60a, i.e., the width WP of the trailing-side end face 60 b in thecross-track direction CT is approximately correspondent to track widthof the recording track of the magnetic disk 12. At the tip section 60 a,the trailing-side end face 60 b and leading-side end face 60 c mayextend in the direction perpendicular to the ABS 43 or may extend in thedirection diagonal to the direction perpendicular to the ABS 43. Theboth side faces 60 d extend diagonal relatively to the central axis lineC, i.e., relatively to the down-track direction DT.

As shown in FIGS. 3 to 6 , the trailing shield 62 is formed of a softmagnetic material and is provided in order to efficiently close themagnetic path through the soft magnetic material layer 102 of themagnetic disk 12 immediately under the main pole 60. The trailing shield62 is arranged on the trailing side of the main pole 60. The trailingshield 62 is formed into an approximately L-shaped member and a tipsection 62 a thereof is formed into a long and thin rectangular shape.The tip-end face of the trailing shield 62 is exposed to the ABS 43 ofthe slider 42. The tip section 62 a includes a leading-side end face(magnetic-pole end face) 62 b opposed to the tip section 60 a of themain pole 60. The leading-side end face 62 b is sufficiently longer thanthe width WP of the tip section 60 a of the main pole 60 and track widthof the magnetic disk 12 and extends in the cross-track direction CT. Theleading-side end face 62 b extends perpendicular to or slightly diagonalto the ABS 43. At the ABS 43, the lower part of the leading-side endface 62 b is opposed to the trailing-side end face 60 b of the main pole60 in parallel with each other with the write gap WG (gap length in thedown-track direction DT) held between them.

As shown in FIG. 4 and FIG. 5 , the trailing shield 62 includes a firstjoint section 50 joined to the main pole 60. The first joint section 50is joined to the upper part of the main pole 60 a through a nonconductor52, i.e., joined magnetically to a part of the main pole 60 separatefrom the ABS 43. The first recording coil 70 is wound around, forexample, the first joint section 50 in the first magnetic core. When asignal is written to the magnetic disk 12, by making a recording currentflow through the first recording coil 70, the first recording coil 70excites the main pole 60 to make a magnetic flux flow through the mainpole 60. A recording current to be supplied to the first recording coil70 and second recording coil 72 is controlled by the main controller 90.

As shown in FIG. 4 and FIG. 6 , the pair of side shields 63 is arrangedin such a manner as to be physically divided into two sections by themain pole 60 and joined to the trailing shield 62. In this embodiment,the side shields 63 are formed of a high permeability material integralwith the tip section 62 a of the trailing shield 62 and protrude fromthe leading-side end face 62 b of the tip end section 62 a toward theleading end side of the slider 42.

As shown in FIGS. 3 to 5 , the leading shield 64 formed of a softmagnetic material is provided on the leading side of the main pole 60 inopposition to the main pole 60. The leading shield 64 is formed into anapproximately L-shaped member and a tip section 64 a thereof on the ABS43 side is formed into a long and thin rectangular shape. The tip endface (lower end face) of the tip section 64 a is exposed to the ABS 43.The trailing-side end face 64 b of the tip section 64 a extends in thecross-track direction CT. At the ABS 43, the trailing-side end face 64 bis opposed to the -leading side end face 60 c of the main pole 60 with agap held between them. In this embodiment, the tip section 64 a of theleading shield 64 is formed of a high permeability material integralwith the side shields 63.

Further, the leading shield 64 includes a second joint section 68 joinedto the main pole 60 at a position separate from the ABS 43. This secondjoint section 68 is formed of, for example, a soft magnetic material,and is joined to an upper part of the main pole through a nonconductor59, i.e., joined magnetically to a part of the main pole 60 separatefrom the ABS 43. Thereby, the second joint section 68 constitutes amagnetic circuit together with the main pole 60 and leading shield 64.The second recording coil 72 of the write head 58 is arranged in such amanner as to be wound around, for example, the second joint section 68,and applies a magnetic field to this magnetic circuit.

As shown in FIG. 5 and FIG. 6 , the STO 65 functioning as ahigh-frequency oscillator element is provided inside the write gap WGand between the tip section 60 a of the main pole 60 and tip section 62a of the trailing shield 62. The STO 65 includes a spin injection layer65 a, intermediate layer (nonmagnetic conductive layer) 65 b, andoscillation layer 65 c, and is formed by stacking these layers from themain pole 60 side to the trailing shield 62 side in the order mentioned,i.e., by stacking these layers in sequence in the down-track directionDT of the magnetic head 16. The spin injection layer 65 a is joined tothe trailing-side end face 60 b of the main pole 60 through thenonmagnetic conductive layer (foundation layer) 67 a. The oscillationlayer 65 c is joined to the leading side end face 62 b of the trailingshield 62 through the nonmagnetic conductive layer (cap layer) 67 b. Itshould be noted that the stacking order of the spin injection layer 65a, intermediate layer 65 b, and oscillation layer 65 c may also beopposite to the above, i.e., these layers may also be stacked insequence from the trailing shield 62 side to the main pole 60 side.

Each of the spin injection layer 65 a, intermediate layer 65 b, andoscillation layer 65 c includes a lamination plane or film surfaceextending in a direction intersecting the ABS 43, for example, directionperpendicular to the ABS 43. The lower end face of at least theoscillation layer 65 c, in this embodiment, the lower end face of thewhole STO 65 including the spin injection layer 65 a, intermediate layer65 b, and oscillation layer 65 c is exposed to the ABS 43 and extendsflush with the ABS 43. Alternatively, the lower end face of the wholeSTO 65 may be positioned in the direction of separation from the ABS 43,e.g., in the direction perpendicular to the ABS 43 and backward from theABS 43, i.e., the lower end face of the whole STO 65 may also bepositioned separate from the ABS 43. Further, the lower end face of theSTO 65 is not limited to a planar surface and may also be formed into anupwardly convex arc-like shape.

As shown in FIG. 6 , at the ABS 43, the width WS of the STO 65 in thecross-track direction CT is formed greater than the width WP of thetrailing-side end face 60 b of the main pole 60 (WS>WP). In one example,the width WS of the STO 65 is made about 1.1 to 1.6 times the width WPof the main pole 60. Further, the STO 65 is arranged in such a manner asto cover at least one of the end edges (ends in the cross-trackdirection) EE1 and EE2 of the trailing-side end face 60 b, i.e., as toextend to the outside of the main pole 60 beyond the end edge. In thisembodiment, the STO 65 is arranged symmetrical relatively to the centralaxis line C, and covers both the end edges EE1 and EE2 of thetrailing-side end face 60 b in the cross-track direction CT. That is,each of the both end sections of the STO 65 in the cross-track directionCT extends to the outside of the main pole 60 beyond the end edge EE1,EE2 of the trailing-side end face 60 b.

As shown in FIG. 4 and FIG. 5 , each of the main pole 60 and trailingshield 62 is connected to the connection terminal 45 through the wiring,and is furthermore connected to the head amplifier IC 30 and maincontroller 90 through the flexure 28. A current circuit through which anSTO drive current (bias voltage) is made to flow in series from the headamplifier IC 30 through the main pole 60, STO 65, and trailing shield 62is formed.

Each of the first recording coil 70 and second recording coil 72 isconnected to the connection terminal 45 through the wiring and isfurthermore connected to the head amplifier IC 30 through the flexure28. The second recording coil 72 is wound in the direction opposite tothe first recording coil 70. When a signal is written to the magneticdisk 12, by making the recording current flow from the recording-currentsupplying circuit 91 of the head amplifier IC 30 to the first recordingcoil 70 and second recording coil 72, the main pole 60 is excited and amagnetic flux is made to flow through the main pole 60. The recordingcurrent to be supplied to the first recording coil 70 and secondrecording coil 72 is controlled by the main controller 90. It should benoted that the second recording coil 72 may also be connected in seriesto the first recording coil 70. Further, the first recording coil 70 andsecond recording coil 72 may also be subjected to current supply controlseparately from each other.

As shown in FIG. 3 , the magnetic head 16 may further be provided with afirst heater 76 a and second heater 76 b. The first heater 76 a isprovided in the vicinity of the write head 58, for example, between thefirst recording coil 70 and second recording coil 72 and in the vicinityof the main pole 60. The second heater 76 b is provided in the vicinityof the read head 54. Each of the first heater 76 a and second heater 76b is connected to the terminal 45 through the wiring, and is furthermoreconnected to the head amplifier IC 30 through the flexure 28.

At the time of an operation of the HDD 10 configured in the mannerdescribed above, the main controller 90 drives the spindle motor 21 bythe driver IC 92 under the control of the MPU 97, and rotates themagnetic disk 12 at a predetermined rotational speed. Further, the maincontroller 90 drives the VCM 22 by the driver IC 92, and moves themagnetic head 16 to a position on a desired track of the magnetic disk12 and carries out positioning of the magnetic head 16. The ABS 43 ofthe magnetic head 16 is opposed to the disk surface with a gap heldbetween them. In this state, read of recorded information from themagnetic disk is carried out by means of the read head 54, and write ofinformation to the magnetic disk 12 is carried out by means of the writehead 58.

At the time of write of information, the bias-voltage supplying circuit93 of the head amplifier IC 30 makes the drive current flow in seriesthrough the connection terminal 45, wiring, main pole 60, STO 65, andtrailing shield 62 by applying a bias voltage to the main pole 60 andtrailing shield 62 under the control of the MPU 97. The drive currentflows in the direction perpendicular to the lamination plane of the STO65. The STO 65 oscillates spin torque, generates a high-frequencymagnetic field, and applies this high-frequency magnetic field to themagnetic recording layer 103 of the magnetic disk 12.

At the same time, the recording-current supplying circuit 91 of the headamplifier IC 30 makes the recording current flow through the first andsecond recording coils 70 and 72 according to the recording signal andrecording pattern generated from the R/W channel 94. The first andsecond recording coils 70 and 72 excite the main pole 60 to generate therecording magnetic field, and apply the perpendicular oriented recordingmagnetic field to the magnetic recording layer 103 of the magnetic disk12 immediately under the main pole 60. Thereby, information is recordedon the magnetic recording layer 103 with a desired track width. Bysuperposing the high-frequency magnetic field of the STO 65 upon therecording magnetic field, the magnetization reversal of the magneticrecording layer 103 is promoted, and magnetic recording of high magneticanisotropic energy can be carried out.

Further, the spin torque oscillated by the STO 65 is directed to adirection opposite to the direction of the gap magnetic field createdbetween the main pole 60 and trailing shield. Accordingly, the spintorque operates to reduce the leakage flux directly flowing from themain pole 60 to the trailing shield 62. As a result, the amount of themagnetic flux flowing from the main pole 60 toward the magneticrecording layer 103 of the magnetic disk 12 is enhanced, and desireddata can be written to the magnetic recording layer 103.

In this embodiment, in the magnetic pole of the magnetic head 16, morespecifically, in the main pole 60 of the write head 58 of the headsection 44, the magnetic pole width is made different according to theposition of the magnetic head 16 (write head 58). The position of themagnetic head in this case is the relative position in the direction inwhich a plurality of magnetic disks 12 are arranged on the same axis atpredetermined intervals, i.e., in the direction (parallel arrangementdirection) in which a plurality of magnetic heads 16 are arranged atpredetermined intervals in such a manner as to be correspondent to thesemagnetic disks 12. Hereinafter, the state where the magnetic disks 12and magnetic heads 16 are arranged in the manner described above isreferred to as a stacked state, and the direction in which the magneticdisks 12 and magnetic heads 16 are arranged at predetermined intervalsis referred to as a stacking direction. That is, the magnetic disks 12and magnetic heads 16 are arranged in the stacking direction in thestacked state. The magnetic pole width is the width of the main pole 60in the cross-track direction CT which is the width direction of therecording track formed in the magnetic recording layer (recording layer)103 of the magnetic disk 12 and is the width WP of the tip section 60 a.

The number of the magnetic heads 16 corresponds to the number of themagnetic disks 12. In FIG. 7 , the configuration in which nine magneticdisks 12 are arranged on the same axis in the stacked state, andeighteen magnetic heads 16 are arranged in the stacked state in such amanner as to be correspondent to both surfaces of the magnetic disks 12on a one-to-one basis is schematically shown as an example.

These magnetic disks 12 are arranged in sequence from the magnetic disk12 a positioned on the base side (lower side in FIG. 7 ) of the housing11 to the magnetic disk 12 i positioned on the cover side (upper side inFIG. 7 ) in the stacked state. Further, in line with the abovecorrespondingly, the magnetic heads 16 are arranged in sequence from themagnetic head 16 a positioned on the base side of the housing 11 to themagnetic head 16 r positioned on the cover side in the stacked state.

The width WP of the main pole 60 is larger in accordance with the degreeof separation of the position of the magnetic head 16 at the outer layerfrom the vicinity of the center in the stacking direction. That is, thelarger the width WP of the magnetic head 16, the farther is the positionof the outer layer (outwardly farther from the vicinity of the center inthe parallel arrangement direction) at which the magnetic head 16 ispositioned from the vicinity of the center in the stacking direction.The center in the stacking direction is the intermediate position in thestacking direction (parallel arrangement direction) specified by theplurality of magnetic heads 16 arranged in the stacked state. To put itanother way, the center in the stacking direction corresponds to theposition of the center (node) of torsion occurring in the shaftrotatably supported by the bearing section 24 of the carriage assembly20.

In the example shown in FIG. 7 , in the eighteen magnetic heads 16 a to16 r, the position between the magnetic heads 16 i and 16 j correspondsto the center in the stacking direction. Accordingly, these magneticheads 16 i and 16 j correspond to the magnetic heads 16 in the vicinityof the center in the stacking direction. Hereinafter, these magneticheads 16 i and 16 j are appropriately referred to as central heads andare discriminated from the other magnetic heads 16. It should be notedthat when the number of the magnetic heads 16 is an odd number, themagnetic head 16 arranged at the center in the stacking directioncorresponds to the central head. Further, the magnetic head 16 a is themagnetic head 16 positioned at the outermost layer on the base side inthe stacking direction, and magnetic head 16 r is the magnetic head 16positioned at the outermost layer on the cover side in the stackingdirection. Hereinafter, these magnetic heads 16 a and 16 r positioned atthe outermost layers are appropriately referred to as outer heads andare discriminated from the other magnetic heads 16.

In the eighteen magnetic heads 16, the width WP of the main pole 60 islarger in the magnetic heads 16 positioned at the outer layers fartherfrom the vicinity of the center in the stacking direction according tothe degree of separation from the center. FIG. 9 is a view showing anexample of a value of a width WP (write core width) of the main pole 60of each of the write heads 58 in the eighteen magnetic heads 16 a to 16r. In FIG. 9 , Head No. 1 corresponds to the magnetic head 16 a, andlikewise Head No. 18 corresponds to the magnetic head 16 in ascendingorder.

As shown in FIG. 9 , the width WP of the main pole 60 is the smallest inthe magnetic heads 16 i and 16 j which are the central heads, andbecomes gradually larger in the magnetic heads 16 positioned on theouter layer side relatively to the central heads in the stackingdirection according to the degree of separation from the central heads,and is the largest in the magnetic heads 16 a and 16 r which are theouter heads. In the example shown in FIG. 9 , although the variation(amount of change) in the width WP (write core width) is expressed inunits of 1 nm, the variation is not limited to the above. Further, thevariations may not necessarily be uniform, and the variation in thewidth WP may be varied from the central heads to the outer heads.

Here, for example, the larger the width WP of the main pole 60, the morefrequently blurred write leaking into the adjacent track occurs easilydue to a plurality of times of repetitive write to the magnetic disk 12.For this reason, adjustment such as setting the track width larger orthe like becomes necessary. Further, the closer the position of themagnetic head 16 to the base side and cover side of the housing 11,i.e., the closer the position of the magnetic head 16 to the outermostlayer side in the stacking direction (on the both sides), the moreliable to be worse is the positioning accuracy of the magnetic head 16.In this case, the closer the position of the magnetic disk 12 to theoutermost layer side on which the positioning accuracy is relatively thelowest, the more liable is write to protrude into the adjacent track byone time of the write operation, and hence it becomes necessary to setthe track pitch larger than those magnetic disks 12 on the inner layerside having relatively higher positioning accuracy.

Conversely, in this embodiment, instead of adjusting the track pitch,the closer the position of the magnetic head 16 to the central head, thesmaller the width WP of the main pole 60 is made and, the closer theposition of the magnetic head 16 to the outer head, the larger the widthof the main pole 60 is made. Accordingly, even when the positioningaccuracy of the outer head becomes lower than the central head accordingto the position of the outer head, it becomes possible to increase therecording capacities of the magnetic disks 12. Magnetic heads 16different from each other in the width WP of the main pole 60 can beintermingled within one HDD 10, and hence it becomes possible to enhancethe yield rate of the magnetic head 16.

As described above, instead of making the width WP of the main pole 60of the magnetic head 16 positioned closer to the central head smalleraccording to the position of the magnetic head 16 and making the widthWP of the main pole 60 of the magnetic head 16 positioned closer to theouter head larger according to the position of the magnetic head 16, bymaking, for example, the width of the magnetic characteristics of themain pole 60 of the magnetic head 16 closer to the central head smalleraccording to the position of the magnetic head 16 and making the widthof the magnetic characteristics of the main pole 60 of the magnetic head16 closer to the outer head larger according to the position of themagnetic head 16, it is also possible to increase the recordingcapacities of the magnetic disks 12. That is, in this case, the largerthe width of the magnetic characteristics of the main pole 60 of themagnetic head 16, the farther the position at the outer layer at whichthe magnetic head 16 is arranged is from the vicinity of the center inthe stacking direction. For example, the width of the magneticcharacteristics of the main pole 60 is the smallest in the magneticheads 16 i and 16 j which are the central heads, and the closer theposition of the magnetic head 16 to the outermost layer side relativelyto the central head in the stacking direction, the larger is the widthof the magnetic characteristics stepwise, and the width of the magneticcharacteristics is the largest in the magnetic heads 16 a and 16 r whichare the outer (outermost) heads. The variations in the width of themagnetic characteristics may not necessarily be uniform, and thevariation in the width of the magnetic characteristics may be variedfrom the central heads to the outer (outermost) heads.

When magnetic recording is carried out with respect to the recordingtrack by using the magnetic head 16, more specifically, by using thewrite head 58, the width of the magnetic characteristics of the mainpole 60 is the width of the recording area in the cross-track directionCT the magnetic characteristics of which can be appropriately read bythe read head 54. Regarding such a width, for example, after anoff-track profile of the recording signal output at the time when thebias voltage of, for example, the STO 65 is turned off is measured asshown in FIG. 8 , the above width is defined as a half value width (50%position) thereof or the like. It should be noted that the value of eachof the cross-track position and signal output shown in FIG. 8 is only anexample, and is not limited to this.

Next, HDDs according to other embodiments will be described. It shouldbe noted that in each of the other embodiments to be described below,the fundamental configuration is equivalent to the first embodiment.Accordingly, in the following descriptions, the characteristicconfiguration of each of the other embodiments different from the firstembodiment will be described, and configurations identical to the firstembodiment are to be referred to the corresponding drawings in the firstembodiment, and descriptions of the configurations are omitted.

Second Embodiment

In the second embodiment, the operation performance of each of themagnetic heads 16 is tested before the magnetic heads 16 areincorporated in the HDD 10, and the magnetic heads 16 are classifiedinto a plurality of groups according to the test results. In thisembodiment, the error rate of the magnetic head 16 is detected. Theerror rate is, in one recording (write) operation of write to therecording track of the magnetic disk 12 by using the write head 58, therate of occurrence of a pattern in which recording (write) protrudesinto a recording track (hereinafter referred to as an adjacent recordingtrack) adjacent to the current recording track.

FIG. 10 is a view schematically showing a relationship between a writecount indicating the number of times of write to the adjacent recordingtrack and error rate. In FIG. 10 , the magnetic heads 16 are classifiedinto three groups A, B, and C, and a relation between the number oftimes of write to the adjacent recording track and error rate after thewrite count in each group is schematically shown. In the examples shownin FIG. 10 , the error rate becomes worse in the order of the group A,group B, and group C. More specifically, as the write count increases,i.e., for example, when the write count exceeds N, deterioration in theerror rate of the group B becomes conspicuous as compared with the groupA, and furthermore, deterioration in the error rate of the group Cbecomes conspicuous as compared with the group B.

In this embodiment, among a plurality of groups of magnetic heads 16classified according to the error rate as described above, the higherthe error rates of the magnetic heads 16 belonging to the group, thefarther is the position of the outer layer (outwardly more separate fromthe vicinity of the center in the parallel arrangement direction) atwhich the group is arranged from the vicinity of the center in thestacking direction.

Here, the configuration in which the eighteen magnetic heads 16 a to 16r are arranged as shown in FIG. 7 is assumed. In this case, thesemagnetic heads 16 a to 16 r are classified into a plurality of groups inunits of a predetermined number according to the error rate. As oneexample, the eighteen magnetic heads 16 a to 16 r are classified inunits of six magnetic heads into three groups A, B, and C correspondingto FIG. 10 . More specifically, the magnetic heads 16 g, 16 h, 16 i, 16j, 16 k, and 16 l belong to the group A. The magnetic heads 16 d, 16 e,16 f, 16 m, 16 n, and 16 o belong to the group B. The magnetic heads 16a, 16 b, 16 c, 16 p, 16 q, and 16 r belong to the group C.

Accordingly, in the configuration example shown in FIG. 7 , the sixmagnetic heads 16 g to 161 belonging to the group A in which the errorrate is the lowest are arranged in the vicinity of the center in thestacking direction. On the base side (positions of the magnetic heads 16d, 16 e, and 16 f) of above these magnetic heads 16 and on the coverside (positions of the magnetic heads 16 m, 16 n, and 16 o), three eachof the magnetic heads 16 belonging to the group B in which the errorrate is the second lowest next to the group A are arranged. Furthermore,on the base side (positions of the magnetic heads 16 a, 16 b, and 16 c)and on the cover side (positions of the magnetic heads 16 p, 16 q, and16 r) three each of the magnetic heads 16 belonging to the group C arearranged.

Thereby, the error rate of the magnetic head 16 becomes higher from thecentral heads to the outer heads group by group in the stackingdirection. It should be noted that the number of groups into which themagnetic heads 16 are classified is not limited to three, and may be twoor four or more. Here, in the magnetic heads 16 arranged in the stackingdirection, the closer to the outer heads, the more liable to be worse isthe positioning accuracy, and it is desirable that the pitch (trackpitch) be made larger. On the other hand, whereas it is necessary towiden the track pitch in the outer heads, it becomes possible to moreeasily alleviate the fringe characteristics (deterioration in the errorrate at the time when magnetic recording is carried out on the adjacenttrack) in the outer heads correspondingly. Further, in the magneticheads in which the error rate is higher as described above, it is alsopossible to reduce the track pitch density by increasing the trackrecording density. Accordingly, in this embodiment, instead of adjustingthe track pitch, the higher the error rates of the magnetic heads 16belonging to the group, the farther is the position of the outer layerat which the group is arranged from the vicinity of the center in thestacking direction. Accordingly, it becomes possible to increase therecording capacities of the magnetic disks 12.

Third Embodiment

In the third embodiment, the operation performance of the magnetic disks12 is tested before the magnetic disks 12 are incorporated in the HDD10, and the magnetic disks 12 are classified into a plurality of groupsaccording to the test results. In this embodiment, an index valueindicating the overwrite characteristics (OW) of the magnetic disks 12is detected. The overwrite characteristics are expressed as an index bya difference between the amplitudes of recording patterns before andafter the overwrite at the time when a recording pattern of a certainfrequency is overwritten with a recording pattern of a frequencydifferent from the frequency of this recording pattern, and thesuperiority or inferiority (difficulty in writing) of the overwritecharacteristics is determined according to the value of the index. Forexample, in the case of perpendicular magnetic recording, it is moredifficult to write a low-frequency signal than to write a high-frequencysignal, and hence it is recommendable to make the value in decibel (dB)by which an unerased remaining signal at the time when a low-frequencysignal is written after a high-frequency signal is written is expressedthe index of the overwrite characteristics.

FIG. 11 is a view showing an example of a case where the magnetic disks12 are classified on the basis of such overwrite characteristics (OW).In the example shown in FIG. 11 , the magnetic disks 12 are classifiedinto five groups according to the range of the value of the overwritecharacteristics, i.e., the degree of difficulty in writing. In thiscase, Gr1 is a group to which the magnetic disks 12 most difficult to beoverwritten belong and, in ascending order, Gr5 is a group to which themagnetic disks 12 easiest to be overwritten belong. It should be notedthat the thresholds of the groups shown in FIG. 11 are only examples andare not limited to the values shown in FIG. 11 , and the thresholds canarbitrarily be set.

In this embodiment, among the plurality of groups into which themagnetic disks 12 are classified according to the overwritecharacteristics (OW) as described above, the higher the overwritecharacteristics of the magnetic disks 12 belonging to the group, thefarther is the position of the outer layer (outwardly farther from thevicinity of the center in the parallel arrangement direction) at whichthe group is arranged from the vicinity of the center in the stackingdirection.

Here, the configuration in which nine magnetic disks 12 a to 12 i arearranged as shown in FIG. 7 is assumed. In this case, these magneticdisks 12 a to 12 i are classified into a plurality of groups in units ofa predetermined number according to the overwrite characteristics. Asone example, the nine magnetic disks 12 a to 12 i are classified intofive groups (Gr1 to Gr5) corresponding to FIG. 11 . More specifically,the magnetic disk 12 e belongs to Gr1 (20≤OW<23). Likewise, the magneticdisks 12 d and 12 f belong to Gr2 (23≤OW<26), magnetic disks 12 c and 12g to Gr3 (26≤OW<29), magnetic disks 12 b and 12 h to Gr4 (29≤OW<32), andmagnetic disks 12 a and 12 i to Gr5 (32≤OW<35), respectively.

Accordingly, in the configuration example shown in FIG. 7 , the magneticdisk 12 e belonging to Gr1 in which the overwrite characteristics arethe lowest is arranged in the vicinity of the center in the stackingdirection. On the base side and cover side of the magnetic disk 12 e,the magnetic disks 12 belonging to Gr2, Gr3, and Gr4 higher than Gr1 inthe overwrite characteristics are respectively arranged. Further, themagnetic disks 12 a and 12 i belonging to Gr5 which is the highest inthe overwrite characteristics are respectively arranged at the outermostlayers in the stacking direction.

Thereby, the overwrite characteristics of the magnetic disks 12 becomehigher group by group from the vicinity of the center in the stackingdirection to each of the outermost layers. Accordingly, for example,unlike the first embodiment and second embodiment described above, evenwhen the widths WP of the main poles 60 of the magnetic heads 16 areapproximately uniform or even when the error rates are approximatelyuniform, it becomes possible to increase the recording capacities of themagnetic disks 12.

Fourth Embodiment

In the fourth embodiment, the head amplifier IC 30 makes the recordingcurrent for exciting the main pole 60 differ according to the positionof the magnetic head 16 (write head 58) in the stacking direction. Morespecifically, at the time of carrying out magnetic recording on themagnetic disk 12 (write of data to the magnetic disk 12), the recordingcurrent to be supplied from the recording-current supplying circuit(recording-current supplying section) 91 to the first recording coil 70and second recording coil 72 is controlled by the main controller 90.

FIG. 12 is a flowchart showing an example of such control(recording-current control processing) of the recording current to becarried out by the main controller 90.

As shown in FIG. 12 , at the time of write of data to the magnetic disk12, the main controller 90 receives a write command to write data to themagnetic disk 12 from the host 95 (ST1).

Upon receipt of the write command, the main controller 90 selects a datawrite destination and specifies a recording track of the magnetic disk12 to which the data is to be written on the basis of servo informationor the like. Thereby, the main controller 90 specifies a position of amagnetic head 16 by which the data is to be written (magneticallyrecorded) to the specified recording track in the stacking direction(parallel arrangement direction) (ST2).

Subsequently, the main controller 90 writes data on the magnetic disk 12specified as the data write destination. More specifically, the HDC 96causes the head amplifier IC 30 to execute signal processing of the datathrough the R/W channel 94. At this time, the head amplifier IC 30varies the magnitude of the recording current to be supplied from therecording-current supplying circuit 91 to the first recording coil 70and second recording coil 72 according to the position of the magnetichead 16 (write head 58) in the stacking direction. Thereby, the mainpole 60 is excited and the amount of the magnetic flux flowing throughthe main pole 60 is varied. In the memory 80 of the main controller 90,for example, a predetermined table in which the position of the magnetichead 16 (write head 58) in the stacking direction and optimum value ofthe recording current at the corresponding position are correlated witheach other as a relationship between the above data items is stored. Atthe time of control of the recording current, the MPU 97 sets theoptimum value of the recording current at the position of the magnetichead 16 (write head 58) in the stacking direction according to the tableand delivers the value to the head amplifier IC 30 as a parameter.

In this embodiment, the recording current supplying circuit 91 controlsthe recording current in such a manner that the closer the arrangementposition of the magnetic head 16 (outer head) to the outermost layerside (outermost side in the parallel arrangement direction) in thestacking direction, the larger is made the recording current forexciting the main pole 60 (of the outer head) than the magnetic head 16(central head) arranged in the vicinity of the center in the stackingdirection (parallel arrangement direction) (ST3). Making the recordingcurrent for exciting the main pole 60 larger exhibits an effectequivalent to increasing the width WP of the main pole 60. Accordingly,by making the recording current for exciting the main pole 60 of theouter head larger than that of the central head according to the degreeof separation of the outer head from the central head, it becomespossible to obtain the effect equivalent to making the width WP of themain pole 60 of the outer head larger than the central head according tothe degree of separation of the outer head from the central head.

Thereby, for example, unlike the first embodiment and second embodimentdescribed above, even when the widths WP of the main poles 60 of themagnetic heads 16 are approximately uniform or even when the error ratesare approximately uniform, it becomes possible to increase the recordingcapacities of the magnetic disks 12. Further, for example, unlike thethird embodiment described above, even when the overwritecharacteristics (OW) of the magnetic disks 12 are approximately uniform,it becomes possible to increase the recording capacities of the magneticdisks 12.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A magnetic disk device comprising: a plurality ofmagnetic disks each including a recording layer and arranged on the sameaxis at intervals in juxtaposition with each other; and a plurality ofmagnetic heads each including a magnetic pole configured to generate arecording magnetic field in a direction perpendicular to the recordinglayer and arranged at intervals in the parallel arrangement direction ofthe magnetic disks in juxtaposition with each other, wherein among aplurality of groups of the magnetic disks classified according to anindex value indicating the overwrite characteristics of the magneticdisk, the higher the index value of each of the magnetic disks belongingto a group, the farther is the group arranged outwardly from thevicinity of the center in the parallel arrangement direction.
 2. Themagnetic disk device of claim 1, wherein the index value is a value indecibel (dB) by which an unerased remaining signal at the time when alow-frequency signal is written after a high-frequency signal is writtenis expressed.
 3. The magnetic disk device of claim 1, wherein in theplurality of magnetic heads, the magnetic pole widths of the magneticpoles in the width direction of the recording track formed in therecording layer are uniform.
 4. The magnetic disk device of claim 1,wherein in the plurality of magnetic heads, the rates of occurrence ofprotrusion of magnetic recording into an adjacent recording trackadjacent to the recording track at the time of magnetic recording on therecording track formed in the recording layer are uniform.